The present invention relates generally to automotive electronic control units, and, in particular, to use of a flexible circuit that is bent in the assembly of an automotive electronic control unit.
Engine mounted electronic control units for automotive engines are disposed in a confined space in an environment subject to high ambient temperatures and extreme vibrations. Typically, in order to enhance thermal performance protect against engine vibrations, a printed circuit board that includes control circuitry is affixed to a rigidizer that may be bent to produce a reduced size module and that also functions as a heat spreader. For example, in a direct engine mount application where a Polybent(trademark) printed circuit board, that is a printed circuit board that has a flexible circuit that is bent, is used for packaging an electronic control unit, the printed circuit board is mounted to an aluminum rigidizer. The rigidizer provides mechanical support for the printed circuit board and assists in the dissipation of heat generated by components on the printed circuit board, which heat is conductively transferred from the components to the underlying rigidizer.
Referring now to FIGS. 1 and 2, an electronic control unit (ECU) 100 of the prior art is illustrated. FIG. 1 is an isometric perspective of an end view of electronic control unit 100. FIG. 2 is a cross-sectional side view of electronic control unit 100. Electronic control unit 100 includes a flexible printed circuit board 104, such as a Polybent(trademark) printed circuit board, that is affixed to a rigidizer 106 by use of a pressure sensitive adhesive (PSA) tape, or film, 202. Typically, circuit board 104 has a number of electronic components 102 mounted on the surface of the circuit board. Adhesive 202 is disposed between rigidizer 106 and printed circuit board 104 and functions to secure the printed circuit board to the rigidizer. After being secured to the rigidizer, the printed circuit board is essentially folded in half, resulting in a folded printed circuit board consisting of two main partitions 204, 208 facing each other and connected to each other by a xe2x80x98Wxe2x80x99-shaped, or serpentine, flexible circuit 206 with a radius of curvature 210 bend that is typically approximately 1 millimeter (mm). For example, circuit substrate 104 may be bent using a Polybent(trademark) process, as described in U.S. Pat. No. 5,998,738, the text of which is hereby incorporated by reference herein.
As the functionality of electronic control units has increased over time, the corresponding circuitry has become increasingly dense and complex. As a result, electronic control units have been migrating from the use of two-layer printed circuit boards, such as printed circuit board 104, to the use of four-layer printed circuit boards. One result of the manufacturing process of four-layer printed circuit boards is a thicker flexible circuit 206, even when the flexible circuit remains a two-layer circuit. Due to the thicker flexible circuit 206, flexible circuit boards are now known to crack and split when bent, resulting a control module that must be discarded. The discarded control modules result in excessive manufacturing costs and waste, especially since the printed circuit boards must be populated with components before being folded.
Therefore, a need exists for a method and apparatus for folding a printed circuit board that will not cause splitting and cracking of the flexible circuit.